Primary amines, pyridoxal and thiols induced separation of the mammalian sperm head and tail at specific sites across the head\p=n-\tail junction. Primary amines and pyridoxal induced head detachment by allowing separation of the inner and outer nuclear envelope membranes adjacent to the tail basal plates. This detachment was prevented by prior reduction with sodium cyanoborohydride. The chemistry of amine\x=req-\ induced head separation and the similar action of pyridoxal indicate that the

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... and tail are joined by Schiff bases formed between proteins within the nuclear membranes. Head detachment with thiols occurred at two sites: across the connecting filaments linking the basal plate and the capitulum of the tail\p=n-\neckcomplex and between the inner nuclear membrane and the nuclear chromatin. Mammalian epididymal spermatozoa exhibited species differences in susceptibility to head detachment induced by hydromechanical shear. The heads of mouse epididymal spermatozoa readily separated from the tails during vortexing whereas those from the vas deferens were resistant to shear. Head separation occurred at the same site as induced by primary amines. Rabbit spermatozoa from all parts of the epididymis were resistant to mechanical shear. Species differences in the mechanical stability of the head\p=n-\tail junction suggest that the intermolecular Schiff bases linking the head and tail can be formed before or during sperm transport in the epididymis and that their formation probably occurs after the appearance of the periodic structures which bridge the inner and outer membranes of the nucleus in the region of the tail basal plate.